Cytokinin is a plant hormone involved in cell division and differentiation of higher plants, and is an important biologically active substance which is known to exert actions such as induction of division of higher plant cells, differentiation from callus or pith to foliage, prevention of etiolation of leaves, fallen leaves and fallen fruit, and defeat of apical dominance (Cytokinins: Chemistry, Activity, and Function, CRC Press (1994)). As a method of controlling physiological phenomena caused by cytokinin, a method comprising giving cytokinin from the outside, a method comprising controlling biosynthesis of cytokinin in a plant body, a method comprising controlling metabolism of cytokinin in a plant body and the like have been proposed.
A chemical substance serving as the active ingredient of a plant growth regulator has been conventionally found by random screening in which a test chemical substance is directly contacted with a plant and then a biological activity of the plant is tested. In this case, after a chemical substance having a useful biological activity is determined, it is necessary to intensively study what kind of mechanism of action there is for the chemical substance to exert its effect and what is targeted by the chemical substance on the molecular level, in order to predict safety and burden on the environment of the chemical substance.